Industrial process control systems are used to monitor and control industrial processes which produce or transfer liquids or the like. In such systems, it is typically important to measure “process variables” such as temperatures, pressures, flow rates, and others. Process control transmitters are used to measure such process variables and transmit information related to the measured process variable back to a central location such as a central control room.
One type of process variable transmitter is a magnetic flowmeter (or mag meter). Magnetic flowmeters measure flow by using Faraday induction, which is an electromagnetic effect. The magnetic flowmeter includes a coil that is energized to generate a magnetic field across a section of a flow conduit, such as a pipe. The magnetic field induces an electromotive force (emf) in the process fluid flow. The induced voltage drop across the process fluid flow is related to the flow velocity, which is proportional to the volumetric flow rate and the cross sectional area of the flow conduit. The voltage drop is generally measured with electrodes that couple to the process fluid, either directly or via capacitive coupling.
Electromagnetic flow measurement techniques are generally applicable to ionic solutions, water-based fluids and other conducting fluids. Illustrative environments where magnetic flowmeters are employed include: hygienic food and beverage production, water treatment facilities, high-purity pharmaceutical manufacturing, and chemical processing, including hazardous and corrosive process fluid flows. Additionally, mag meters are also employed in the hydrocarbon fuel industry, including hydrocarbon extraction and processing as well as hydraulic fracturing techniques utilizing abrasive and corrosive slurries.
Magnetic flowmeters provide fast and accurate flow measurements in applications where other flow measurement techniques, which introduce a flow measurement element (such as an orifice plate) into the process fluid flow, are not suitable. One of the significant costs in the manufacture of the magnetic flowmeter is the flowtube through which the process fluid flows. This flowtube must bear the process fluid pressure and must not introduce leaks into the process. Typically, the flowtube includes a pair of flanges that bolt to pipe flanges to create a robust process fluid connection. However, in some environments, the added cost of the flanged flowtube may be cost prohibitive. In such instances, a flangeless, or wafer-type magnetic flowmeter is used. The wafer-type magnetic flowmeter includes a flowtube without any flanges. Thus, a wafer-type magnetic flowmeter can be more economical, compact and lightweight than traditional flanged magnetic flowmeters. One example of a commercially available wafer-type magnetic flow sensor is sold under the trade designation Model 8711 Wafer Sensor, available from Emerson Process Management. When a magnetic wafer sensor is paired with suitable transmitter electronics, such as those sold under trade designations, Model 8732E, Model 8712E, or 8712H, a fully operational wafer-type magnetic flowmeter is provided.